Implantable medical devices (IMDs) are devices designed to be implanted into a patient. Some examples of these devices include cardiac function management (CFM) devices such as implantable pacemakers, implantable cardioverter defibrillators (ICDs), cardiac resynchronization devices, and devices that include a combination of such capabilities. The devices are typically used to treat patients using electrical or other therapy or to aid a physician or caregiver in patient diagnosis through internal monitoring of a patient's condition. The devices may include one or more electrodes in communication with one or more sense amplifiers to monitor electrical heart activity within a patient, and often include one or more sensors to monitor one or more other internal patient parameters. Other examples of implantable medical devices include implantable diagnostic devices, implantable drug delivery systems, or implantable devices with neural stimulation capability.
Several types of CFMs provide pacing to one or more ventricles of a patient or subject under a conventional dual chamber DDD pacing mode. In DDD mode, the CFM device is able to provide pacing and sensing to both the atrium and ventricle, and is able to coordinate activity in one heart chamber according to events in the other. For example, the CFM device is able to pace the ventricle according to a timing relationship of paced or sensed events in the atrium. However, unnecessary ventricular pacing may be associated with an increased risk of heart failure and atrial fibrillation in patients with dual chamber CFM devices such as pacemakers and ICDs.